1. Field of the Invention
The invention relates to self-adhesive, thermally crosslinkable 1-component silicone compositions having a long shelf-life, to silicone elastomers obtainable therefrom, and to their use in manufacturing composite moldings.
2. Background Art
The adhesion of crosslinked silicone elastomers to numerous substrates, such as plastics, metals and glasses, is known to be low, i.e. if an addition-crosslinking silicone elastomer material is applied to a substrate and then crosslinked, the resulting silicone elastomer can, as a rule, be peeled away from the substrate surface without difficulty, i.e. by application of but slight tensile forces. Frequently, spontaneous delamination of the silicone elastomer from the substrate may occur. However, since strong and permanent adhesion of the silicone elastomer to the substrate is of decisive importance in numerous applications, a large number of special measures have been proposed for obtaining a strong bond between substrate and silicone elastomer.
In principle, the adhesive strength of the silicone elastomer/substrate laminate can be increased by suitably modifying the chemical and/or physical characteristics of the substrate or of the substrate surface prior to application of the crosslinking silicone elastomer composition. Modification can be effected, for example, by pretreating the substrate surface with adhesion-promoting additives (i.e. primers), by plasma treatment of the substrate surface, by mixing special additives into the substrate, by controlling the morphology of the substrate, by increasing the surface roughness, etc. These measures have, inter alia, the disadvantage that additional process steps are required or the characteristics of the substrate have to meet special requirements.
In the case of high temperature-crosslinking systems, the adhesive strength of the silicone elastomer/substrate composite can be increased by changing the chemical and/or physical characteristics of the addition-crosslinking silicone elastomer material in a controlled manner. Numerous adhesion-promoting additives are known which when mixed with the uncrosslinked silicone material, give rise to self-adhesion of the resulting silicone elastomer on various substrates. These include compounds which contain highly reactive functional groups, such as alkoxy, epoxy, carboxyl, amino, etc., these groups generally being chosen such that the adhesion promoter is capable of reacting both with the substrate and with a silicone elastomer constituent. Although such adhesion promoters may make it possible to dispense with pretreatment of the substrate, the adhesive strength obtained frequently is not satisfactory. Furthermore, the adhesive strength can be increased only to a limited extent by higher adhesion promoter content since the highly reactive groups contained in the adhesion promoter have an increasingly adverse effect on performance characteristics such as shelf-life, crosslinking characteristics (inhibition), toxicology, etc. For these reasons, interest tends to be focused on keeping the content of adhesion promoters as low as possible.
EP-A-686 671 describes a self-adhesive addition-crosslinking material which manages without special adhesion promoters due to the presence of unique reactive polymer constituents. The adhesion-promoting constituent is either an organohydrogenpolysiloxane with minimally two SiH groups on average and whose monovalent Si-bonded radicals consist of at least 12 mol % of hydrocarbon radicals having an aromatic ring, or is a compound with at least one SiH group on average and which contains a group consisting of two aromatic rings, the two aromatic rings being separated from one another by xe2x80x94R13R14Sixe2x80x94, xe2x80x94R13R14SiOxe2x80x94, xe2x80x94OR13R14SiOxe2x80x94 or xe2x80x94R13R14SiOR13R14Sixe2x80x94 and the radicals R13 and R14 being monovalent hydrocarbon radicals. The adhesion-promoting constituent can thus simultaneously be the crosslinking agent of the silicone elastomer material. Good adhesion to organic plastics (especially ABS) is achieved with this composition, while at the same time easy demoldability is exhibited from metallic vulcanization molds, i.e. chromium- or nickel-plated steel molds or mold produced from aluminum alloy.
The high content of 12 mol % or more of radicals containing aromatic rings in the SiH-containing, adhesion-promoting constituent of the compositions of EP-A-686 671, however, results in considerable incompatibility with the other constituents of the addition-crosslinking silicone elastomer material, leading on the one hand, to partial separation (exudation) during storage, necessitating repeated homogenization of the constituent-containing component before use. This incompatibility, which is evident simply from a milky haze in the uncrosslinked material, also manifests itself in substantially reduced transparency of the silicone elastomer parts produced therefrom. If the adhesion-promoting constituent simultaneously acts as a crosslinking agent of the silicone elastomer composition, the incompatibility leads to vulcanization disturbances which result in inhomogeneous network formation and poor mechanical vulcanization properties. In order to overcome these vulcanization disturbances, an SiH-containing crosslinking agent completely compatible with the silicone elastomer material must be used in addition to the adhesion-promoting SiH-containing constituent, which however results in other disadvantages, for example higher compression set, and higher tendency to exude the adhesion-promoting constituent. The high content of aromatic radicals in the SiH-containing, adhesion-promoting constituent also causes a considerable structural viscosity and thixotropy of the silicone elastomer material, which is undesirable in numerous applications for example in injection molding and in liquid silicone rubber. Moreover, the curable silicone mixture of EP-A-686 671 has a very limited shelf-life, so that metering of the platinum catalyst or mixing with the H-siloxane component must occur only a few minutes to hours prior to vulcanization. Finally, the adhesion of this composition to metals is also insufficient.
EP-A-875 536 describes a self-adhesive addition-crosslinking silicone rubber blend which is distinguished in that the SiH crosslinking agent contains at least 20 SiH groups, the remaining radicals being aliphatically saturated; the composition contains an epoxy-functional alkoxysilane and/or alkoxysiloxane; and further optionally a peroxide. The use of glycidyloxypropyltrimethoxysilane (Glymo) is particularly preferred. The silicone rubber blend described in EP-A-875 536 is suitable in particular for the production of composite moldings which consist of the silicone elastomer and an organic plastic. However, the composition described in EP-A-875 536 has the disadvantage that sufficient adhesive strength can be achieved only with the use of very Si-rich crosslinking agents having on average at least 20 SiH groups per molecule. For instance, the crosslinking agents exemplified in the examples have 30 SiH groups per molecule. The use of such high-functionality crosslinking agents reduces the shelf-life of addition-crosslinking silicone rubber blends considerably, i.e. the flowability is greatly impaired, which can lead to stiffening of the material. As a result, proper processing of the material, for example by injection molding, is no longer possible. In addition, relatively large amounts of epoxy-functional alkoxysilane/alkoxysiloxane have to be used in order to achieve a high adhesive strength, with the result that the crosslinking rate is considerably reduced. Although this can partly be compensated by employing a peroxide, as described in EP-A-875 536, only peroxides having a low initiation temperature, such as the disclosed 2,4-dichlorobenzyl peroxide, are suitable for this purpose owing to the necessarily low crosslinking temperature (softening of the organic plastic). These peroxides are both toxicologically suspect owing to the cleavage and secondary products liberated (PCB problems), and further adversely affect the shelf-life of the material. Moreover, these blends can be stored for only a relatively short time, with pot lives in the range of minutes, so that no 1-component products for processing by composite producers can be made available therefrom, but only 2-component or A/B systems.
In the case of addition-crosslinking silicone materials, however, 2-component systems are associated with numerous disadvantages, for example, complicated logistics and a high danger of contamination, in particular of the platinum component or of A/B components with one another, so that partial crosslinking may inadvertently occur during storage. Moreover, an additional step for mixing A and B components is required, which leads to a very sensitive intermediate. This necessitates immediate processing and frequent cleaning of the metering plants, mixing and processing machines, etc., since the material remaining as a result of back-mixing or adhesion to surfaces gels relatively rapidly.
EP-A-1 041 117 describes a readily adhering addition crosslinkable 1-component silicone elastomer composition which contains an organopolysiloxane having both SiH and alkenyl groups and a compound having both alkenyl and hydroxyphenyl groups in the same molecule. The preparation of such silicone elastomer compositions is very complicated and therefore not economical. Moreover, this 1-component blend, too, does not have a long shelf-life but has to be processed rapidly after addition of the platinum catalysts described. It thus also has disadvantages in terms of logistics and cleaning, as in the case of A/B systems.
EP-A-1 045 006 discloses improvement of adhesion in highly viscous, peroxide-crosslinkable silicone elastomer materials (HTV), wherein silatrane derivatives, for example silatrane derivatives of a mixture 2-hydroxyethylamine, methyltrimethoxysilane, and allyl glycidyl ether, are added to the silicone rubber blend in order to obtain good adhesion to organic resins such as PBT or FPP, during vulcanization. Such additives are, however, toxicologically unsafe, both during incorporation in the plant and during the production and use of the composite, since they can release aggressive cleavage products.
In summary, it may be stated that none of the conventional addition-crosslinking silicone elastomer compositions satisfactorily meet the requirements set for a self-adhesive silicone elastomer material which is to be used in particular for the production of composite moldings or for the encapsulation of electrical/electronic parts, namely:
a) good processibility and shelf-life,
b) high crosslinking rate at relatively low temperatures,
c) high adhesive strength on organic plastics, metals and glasses,
d) easy demoldability from vulcanization molds,
e) toxicological safety, and
f) high level of performance characteristics, i.e. transparency, noncorrosiveness, good mechanical and/or electrical property profiles.
It would be desirable to provide a heat-crosslinkable 1-component silicone elastomer material which has good self-adhesion to organic plastics, metals and glasses, which does not have the disadvantages discussed previously and which meet the above requirements.
The invention pertains to self-adhesive, thermally crosslinkable, 1-component silicone compositions comprising an alkenyl-functional diorganopolysiloxane (A), a specific filler or mixture of fillers (B), an SiH-functional organohydrogenpolysiloxane (C), a hydrosilylation catalyst or peroxide crosslinking agent (E), and an organosilicon compound (D) bearing two different functional groups, one group being a vinyl radical or an epoxy or (meth)acryloyloxy group, and one group being a hydrolyzable group.
Diorganopolysiloxane (A) comprises the general formula (1)
R1aR2bSiO(4xe2x88x92axe2x88x92b)/2xe2x80x83xe2x80x83(1),
in which
R1 is a hydroxyl radical or a monovalent, optionally halogen-substituted C1-20 hydrocarbon radical optionally containing O, N, S or P atoms, and being free of aliphatically unsaturated groups,
R2 is a monovalent, aliphatically unsaturated, optionally halogen-substituted C2-10 hydrocarbon radical optionally containing O, N, S or P atoms,
b denotes values from 0.003 to 2,
with the proviso that 1.5 less than (a+b) less than 3.0, that on average at least two aliphatically unsaturated radicals R2 are present per molecule and that the viscosity of the diorganopolysiloxane (A), determined at 25xc2x0 C., is at least 100 Pa.s,
(B) a filler which is selected from filler (B1) having a specific surface area of at least 50 m2/g, aluminum hydroxide (B2), and mixtures thereof,
(C) an organohydrogenpolysiloxane of the general formula (2)
R3cR4dR5eHfSiO(4xe2x88x92cxe2x88x92dxe2x88x9223xe2x88x92f)/2xe2x80x83xe2x80x83(2),
in which
R3 is a monovalent aliphatically saturated C1-20 hydrocarbon radical,
R4 is (a) an optionally halogen-substituted monovalent C6-15 hydrocarbon radical which contains at least one aromatic C6-ring, or (b) a halogen-substituted, saturated monovalent C2-20 hydrocarbon radical optionally containing O, N, S or P atoms,
R5 is a bivalent, optionally halogen-substituted C6-20 hydrocarbon radical Si-bonded at both ends, optionally containing O, N, S or P atoms,
e denotes 0 or a positive integer,
c, d, and f denote positive numbers, with the proviso that the organohydrogenpolysiloxane (B) contains on average 3 to less than 20 SiH groups per molecule, that the relationship: 0.05 less than 100 (d+e)/(c+d+e+f) less than 12 is fulfilled, and that the viscosity of the organohydrogenpolysiloxane (B), determined at 25xc2x0 C., is 1 mPa.s to 100 Pa.s,
(D) an organosilicon compound of the general formula (3)
R7gR8hR9iSiO(4xe2x88x92gxe2x88x92hxe2x88x92i)/2xe2x80x83xe2x80x83(3)
and/or its partial hydrolysis products, in which
R7 is a hydrogen radical, a hydroxyl radical or an optionally halogen- or cyano-substituted, monovalent saturated C1-20 hydrocarbon radical optionally containing O, N, S or P atoms,
R8 is a vinyl radical or an optionally halogen-substituted monovalent C2-20 hydrocarbon radical containing at least one epoxy group or substituted by at least one acryloyloxy or methacryloyloxy group, optionally containing O, N, S or P atoms,
R9 is a hydrolyzable monovalent optionally halogen-substituted C1-20 hydrocarbon radical bonded to Si via an Sixe2x80x94Oxe2x80x94Cxe2x80x94, Sixe2x80x94Oxe2x80x94Nxe2x80x94 or Sixe2x80x94N-link, optionally containing O, N, S or P atoms, with the proviso that 4 greater than gxe2x89xa70, 4 greater than h greater than 0, 4 greater than i greater than 0, 4xe2x89xa7(h+1) greater than 0 and 4xe2x89xa7(g+h+i), and
(E) a hydrosilylation catalyst or peroxide crosslinking agent,
the Mooney viscosity of the silicone compositions, determined at 25xc2x0 C. according to DIN 53523 Part 3, being 20 to 200.
In the silicone compositions, organohydrogenpolysiloxane (C) acts as an adhesion promoter and, in the case of addition-crosslinkable silicone compositions, simultaneously as a crosslinking agent.
The advantageous properties of the silicone compositions consist in the fact that the self-adhesion after vulcanization is achieved by a constituent contained in every addition-crosslinking material, namely the SiH-containing crosslinking agent (C), in combination with the organosilicon compound (D) having epoxy-, acryloyloxy-, methacryloyloxy- and/or vinyl-functional and hydrolyzable radicals, it merely being necessary for the SiH crosslinking agent (C) to contain a few groups which reduce the compatibility with the other constituents of the material (especially with the diorganopolysiloxane (A)). These latter groups are not reactive functional groups but are preferably inert phenyl groups, with the result that the toxicological safety of the material (e.g. drinking water approval; BGA/FDA approval) is preserved, no vulcanization problems occur, the shelf-life is sufficient, the transparency or translucency of the crosslinked silicone elastomer is maintained, and no constituents which exude or are extractable are added. The combination of the SiH crosslinking agent (C), having reduced compatibility, with an organosilicon compound (D) having epoxy-, vinyl-, acryloyloxy- and/or methacryloyloxy-functional and hydrolyzable radicals, makes it possible, first, to keep the content of incompatible groups in the SiH crosslinking agent low, and secondly, to achieve the adhesion-promoting activity of the organosilicon compound (D) having epoxy-, vinyl-, acryloyloxy- and/or methacryloyloxy-functional and hydrolyzable radicals, even in the case of relatively low SiH functionality of the SiH crosslinking agent. Only the combination of the two constituents (C) and (D) leads to synergistic self-adhesion effects of these two constituents.
In particular, the present composition is distinguished by the fact that
a) the crosslinking rate is scarcely reduced,
b) the transparency or color of the crosslinked silicone elastomers is not impaired,
c) there is no need to accept any disadvantageous changes in the mechanical elastomer properties,
d) the adhesion-promoting constituent (C) in the case of addition-crosslinkable composition simultaneously acts as a crosslinking agent (no additional SiH crosslinking agent required),
e) strong self-adhesion can be achieved even on metals without hindering the demoldability from metal vulcanization molds, i.e. adhesion to metal shortly after crosslinking permits demolding of the silicone elastomer part whereas if the adhesively bonded silicone elastomer/metal composite is stored, the silicone elastomer becomes strongly and permanently adhered onto the metal surface within a short time, and
f) the flowability or processibility of the uncrosslinked material is minimally impaired.
Although the adhesion-promoting constituent (C) of the present invention also has reduced compatibility with the other constituents of the material, which is evident from turbidity upon mixing, this turbidity disappears completely as soon as the material is heated for the purpose of crosslinking, indicating a homogeneous distribution of the molecules throughout the crosslinking agent in the material at the time of crosslinking.
If the adhesion-promoting SiH-containing constituent (C) contains phenyl groups in at least 12 mol % of the radicals, however, this turbidity also persists at customary crosslinking temperatures and indicates inhomogeneous network formation, which can also be demonstrated on the basis of the optical properties, the crosslinking characteristics and the mechanical properties.
Examples of the radicals R1 are alkyl radicals such as the methyl, ethyl, propyl, isopropyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, n-octyl, 2-ethylhexyl, 2,2,4-trimethylpentyl, n-nonyl and octadecyl radicals; cycloalkyl radicals such as the cyclopentyl, cyclohexyl, cycloheptyl, norbornyl, adamantylethyl or bornyl radicals; aryl or alkaryl radicals such as the phenyl, ethylphenyl, tolyl, xylyl, mesityl or naphthyl radicals; aralkyl radicals such as the benzyl, 2-phenylpropyl or phenylethyl radicals, and derivatives of the above radicals which are halogenated and/or functionalized with organic groups such as the 3,3,3-trifluoropropyl, 3-iodopropyl, 3-isocyanatopropyl, aminopropyl, methacryloyloxymethyl or cyanoethyl radicals. Preferred radicals R1 contain 1 to 10 carbon atoms and optionally halogen substituents. Particularly preferred radicals R1 are the methyl, phenyl and 3,3,3-trifluoropropyl radicals, in particular the methyl radical.
The radicals R2 are reactive in a hydrosilylation reaction. Examples of these are alkenyl and alkynyl radicals, such as the vinyl, allyl, isopropenyl, 3-butenyl, 2,4-pentadienyl, butadienyl, 5-hexenyl, undecenyl, ethynyl, propynyl and hexynyl radical; cycloalkenyl radicals, such as the cyclopentenyl, cyclohexenyl, 3-cyclohexenylethyl, 5-bicycloheptenyl, norbornenyl, 4-cyclooctenyl or cyclooctadienyl radical; alkenyl aryl radicals, such as the styryl or styrylethyl radical, and derivatives of the above radicals which are halogenated and/or contain heteroatoms, such as the 2-bromovinyl, 3-bromo-1-propynyl, 1-chloro-2-methylallyl, 2-(chloromethyl)allyl, styryloxy, allyloxypropyl, 1-methoxyvinyl, cyclopentenyloxy, 3-cyclohexenyloxy, acryloyl, acryloyloxy, methacryloyl or methacryloyloxy radicals. Preferred radicals R2 are the vinyl, allyl and 5-hexenyl radicals, in particular the vinyl radical.
In the case of the diorganopolysiloxanes (A) of the general formula (1), the viscosity determined at 25xc2x0 C. is preferably at least 1,000 Pa.s, more preferably at least 10,000 Pa.s, preferably not more than 1,000,000 Pa.s, and more preferably not more than 100,000 Pa.s.
Filler (B) is incorporated into the silicone composition in order to achieve a sufficiently high mechanical and/or electrical strength of the crosslinked silicone rubber. Filler (B1) having a specific surface area of at least 50 m2/g, in particular 100 to 400 m2/g, determinated by the BET method, has an active reinforcing effect. The actively reinforcing fillers (B1) are preferably precipitated and/or pyrogenic silica. Filler (B2) is aluminum hydroxide, which is also referred to as alumina trihydrate, preferably having a specific surface area of at least 2 m2/g, in particular 3 to 50 m2/g, according to the determination by the BET method.
Aluminum hydroxide (B2) having a particle size of 0.1 to 50 xcexcm, preferably 1 to 30 xcexcm, is preferably used and improves the electrical insulation properties and the flammability. The aluminum hydroxide (B2) may be untreated or surface-treated with vinylsilanes, such as, for example, Martinal(copyright) 104S from ALUSUISSE, Martinswerk S. A. and Hymod(copyright) 632 or 632 SP from Huber, USA.
The silanization of aluminum hydroxide (B2) can also be carried out during the preparation of the mixture itself, by first introducing the untreated aluminum hydroxide (B2) into the diorganopolysiloxane (A) and then metering in preferably 0.1 to 3% by weight, in particular 0.2 to 2% by weight, based on untreated aluminum hydroxide (B2) of a hydrolyzable vinyl compound, such as vinyltriethoxy- or vinyltrimethoxysilane or divinyltetramethyldisilazane, preferably at 50 to 150xc2x0 C. Corresponding amounts of difunctional vinyl compounds, such as methylvinyldialkoxysilanes or short-chain SiOH-rich vinylmethylsiloxanes, which can be prepared via an upstream hydrolysis of a methylvinylsilane, are also suitable.
The viscosity of the mixture of diorganopolysiloxane (A) and filler (B) is preferably at least 40,000 Pa.s, more preferably at least 80,000 Pa.s.
Examples of R3 are alkyl radicals such as the methyl, ethyl, propyl, isopropyl, tert-butyl, n-octyl, 2-ethyhexyl and octadecyl radicals, and cycloalkyl radicals such as the cyclopentyl, cyclohexyl, norbornyl or bornyl radicals. Preferred radicals R3 are hydrocarbon radicals having 1 to 10 carbon atoms. A particularly preferred radical R3 is the methyl radical.
Examples of R4 (a) are the phenyl, tolyl, xylyl, biphenylyl, anthryl, indenyl, phenanthryl, naphthyl, benzyl, phenylethyl or phenylpropyl radicals, and derivatives of the above radicals which are halogenated and/or functionalized with organic groups, such as the o-, m- or p-chlorophenyl, pentafluorophenyl, bromotolyl, trifluorotolyl, phenoxy, benzyloxy, benzyloxyethyl, benzoyl, benzoyloxy, p-tert-butylphenoxypropyl, 4-nitrophenyl, quinolyl or pentafluorobenzoyloxy radicals.
Examples of hydrocarbon radicals R4 (b) having 2 to 20 carbon atoms are the 3-chloropropyl, 3-bromopropyl, 3,3,3-trifluoropropyl, 2-fluoroethyl, 1,1-dihydroperfluorododecyl and 2-cyanoethyl radicals. Particularly preferred radicals R4 are the phenyl radical and the 3,3,3-trifluoropropyl radical.
Preferred radicals R5 correspond to the general formula (4)
xe2x80x94(O)sxe2x80x94(R6)txe2x80x94(O)uxe2x80x94(X)wxe2x80x94(O)uxe2x80x94(R6)txe2x80x94(O)sxe2x80x94xe2x80x83xe2x80x83(4)
in which
s, t, u and w, independently of one another, denote the values 0, 1 or 2,
R6 may be identical or different and denote a bivalent, optionally halogen-substituted hydrocarbon radical which optionally contains O, N, S or P atoms, is free of aliphatically unsaturated groups and contains 1 to 10 carbon atoms, such as xe2x80x94CH2xe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94CF2xe2x80x94, xe2x80x94CH2xe2x80x94CF2xe2x80x94, xe2x80x94CH2xe2x80x94CHxe2x80x94(CH3)xe2x80x94, xe2x80x94C(CH3)2xe2x80x94, xe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94, xe2x80x94C(CH3)2, xe2x80x94CH2xe2x80x94CH2xe2x80x94CHxe2x80x94Oxe2x80x94xe2x80x94CF2xe2x80x94CF2xe2x80x94Oxe2x80x94,
xe2x80x94(X)xe2x80x94 denotes a bivalent radical which is selected from xe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94Oxe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94Sxe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94SO2xe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94C(CH3)2xe2x80x94Phxe2x80x94, xe2x80x94PhC(CF3)2xe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94C(O)xe2x80x94Phxe2x80x94, cyclohexylene or norbornylene, xe2x80x94Phxe2x80x94 designating a phenylene group. A particularly preferred radical R5 is the phenylene radical.
The organohydrogenpolysiloxane (C) preferably contains 5 to 18 SiH groups per molecule. The viscosity of the constituent (C), measured at 25xc2x0 C., is preferably 2 mPa.s to 1 Pa.s. Owing to the labile nature of the SiH group, the constituent (C) may have a low content, typically less than 100 ppm by weight, of Si-bonded OH groups, arising from the preparation.
Examples of the hydrocarbon radicals R7 are alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, n-octyl, 2-ethylhexyl, 2,2,4-trimethylpentyl, n-nonyl and octadecyl radicals; cycloalkyl radicals such as the cyclopentyl, cyclohexyl, cycloheptyl, norbornyl, adamantylethyl or bornyl radicals; aryl radicals such as the phenyl, ethylphenyl, tolyl, xylyl, mesityl or naphthyl radicals; aralkyl radicals such as the benzyl, phenylethyl or phenylpropyl radicals; alkenyl or alkynyl radicals such as the vinyl, allyl, isopropenyl, 3-butenyl, 2,4-pentadienyl, butadienyl, 5-hexenyl, undecenyl, ethynyl, propynyl and hexynyl radicals; cycloalkenyl radicals such as the cyclopentenyl, cyclohexenyl, 3-cyclohexenylethyl, 5-bicycloheptenyl, norbornenyl, 4-cyclooctenyl or cyclooctadienyl radicals; aralkenyl radicals such as the phenylethenyl and phenylethynyl radical; and derivatives of the above radicals which are halogen-substituted and/or contain heteroatoms, such as the 3-chloropropyl, 3-bromopropyl, decafluoro-1,1,2,2-tetrahydrooctyl, (p-chloromethyl)phenyl, (p-chloromethyl)phenethyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, 2-bromovinyl, 2-allyloxymethyl, acetyl, acetoxymethyl, acetoxyethyl, acetoxypropyl, 3-phenoxypropyl, benzoyloxypropyl, mercaptopropyl, cyanoethyl, cyanopropyl, 3-cyanobutyl, 3-isocyanatopropyl, 2-(carbomethoxy)ethyl, 10-(carbomethoxy)decyl, 2-(carboxymethylthio)ethyl, 3-carboxypropyl, aminomethyl, aminoethyl, aminopropyl, aminohexyl, aminoethylaminopropyl, 3-(N-allylamino)propyl, (aminoethylaminomethyl)phenethyl, m-aminophenyl, 3-(m-aminophenoxy)propyl, 3-acryloyoxypropyl, 3-acryloyloxy-2-hydroxypropyl, 4-(acryloyloxymethyl)phenethyl, methacryloyloxymethyl, methacryloyloxyethyl and methacryloyloxypropyl radicals. Preferred radicals R7 are the methyl, ethyl, propyl, butyl, octyl, vinyl, allyl, phenyl, 3,3,3-trifluoropropyl and cyanopropyl radicals. Particularly preferred radicals R7 are the methyl, vinyl and phenyl radicals.
Examples of the radicals R8 containing epoxy groups are the epoxyethyl, 2,3-epoxypropyl, 3,4-epoxybutyl, 5,6-epoxyhexyl, 9, 10-epoxydecyl, glycidyloxy, 3-glycidyloxypropyl, glycidyloxyisobutyl, 2-methylglycidyloxypropyl, 3-phenylglycidyloxypropyl, glycidyloxyphenylnonyl, glycidyloxybenzylethyl, 3,4-epoxycyclohexyl, 2-(3,4-epoxycyclohexyl)ethyl, 3-(3,4-epoxycyclohexyl)propyl, 1,4-epoxycyclohexyl and 2-(1,4-epoxycyclohexyl)ethyl radicals. Preferred radicals R8 are the 3,4-epoxycyclohexyl, 3-(3,4-epoxycyclohexyl)propyl and glycidyloxypropyl radicals. Radical R8 preferably has 2 to 10 carbon atoms. A particularly preferred radical R8 is the glycidyloxypropyl radical.
Examples of the monovalent hydrocarbon radicals substituted by an acryloyloxy or methacryloyloxy group and having 2 to 20 carbon atoms are mentioned above for R7. Hydrocarbon radicals which have no heteroatoms, in particular having 2 to 10 carbon atoms, such as ethyl, propyl or butyl radicals, are preferred.
Examples of the radicals R9 are
a) alkoxy, enoxy or aryloxy groups of the general formula xe2x80x94OR10, such as the methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, 2-ethylbutoxy, 2-ethylhexyloxy, vinyloxy, allyloxy, isopropenyloxy, cyclobutenyloxy, cyclohexenyloxy, 1,3-butadienyloxy, propargyloxy, phenoxy, benzyloxy, and m- or p-vinylbenzyloxy radicals;
b) acyloxy groups of the general formula xe2x80x94OCOR10, such as the formyloxy, acetoxy, 2-ethylhexanoyloxy, acryloyloxy, methacryloyloxy, benzoyloxy and norbornylacetoxy radicals;
c) amino groups of the general formula xe2x80x94NH2, xe2x80x94NHR10 or xe2x80x94NR102, such as the dimethylamino, diisopropylamino, allylamino, n-butylamino, sec-butylamino and cyclohexylamino radicals;
d) oxime groups of the general formula xe2x80x94ONxe2x95x90CH2, xe2x80x94ONxe2x95x90CHR10 or xe2x80x94ONxe2x95x90CR102, such as the methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl n-amyl ketoxime, and dimethyl ketoxime radicals;
e) amido groups of the general formula xe2x80x94NHxe2x80x94C(xe2x95x90O)xe2x80x94R10 or xe2x80x94NR10xe2x80x94C(xe2x95x90O)xe2x80x94R10, such as the N-methylbenzamido or N-methylacetamido radicals;
f) aminoxy groups of the general formula xe2x80x94ONH2, xe2x80x94ONHR10 or xe2x80x94ONR102, such as the hydroxylamino radical; or
g) those derivatives of the abovementioned radicals which are halogen-substituted and/or contain heteroatoms or have a more complex composition, such as the p-aminophenoxy, 2-methoxyethoxy, 1-methoxy-2-propoxy, 1-methoxyisopropenyloxy, methoxyethoxyethoxy, 1-methoxy-2-methylpropenyloxy, acryloyloxymethoxy, meth-acryloyloxy-(polyethyleneoxy), furyloxy or N-vinylformamido radical and xe2x80x94O-Ph-C(xe2x95x90O)-Ph, xe2x80x94Oxe2x80x94C(CF3)xe2x95x90CHxe2x80x94Cxe2x95x90O)xe2x80x94CF3, xe2x80x94Oxe2x80x94C(CH3xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94CH3, xe2x80x94Oxe2x80x94C(CH3)2xe2x80x94CHxe2x95x90CH2, xe2x80x94NHxe2x80x94C(xe2x95x90O)xe2x80x94CH3, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CH2Br, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CF3, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Cxe2x89xa1CH or xe2x80x94Oxe2x80x94CH2xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94Si(CH3)3,
where the radicals R10 represent monovalent aliphatic or aromatic, saturated or unsaturated, optionally halogen-substituted hydrocarbon radicals having 1 to 10 carbon atoms. Preferred radicals R9 are the alkoxy radicals such as the methoxy, ethoxy, propoxy and butoxy radicals. The particularly preferred radical R9 is the methoxy radical.
Preferred as organosilicon compound (D), are organofunctional silanes, glycidyloxypropyltrimethoxysilane (Glymo), vinyltrimethoxysilane, vinyltriethoxysilane and methacryloyloxypropyltrimethoxysilane being particularly preferred.
The radicals R1 to R10 in all above formulae may be identical or different. Preferred heteroatoms are N, O and S. Preferred halogen substituents are F, Cl and Br.
Hydrosilylation catalyst (E) serves as a catalyst for the addition reaction, termed a hydrosilylation, between the aliphatically unsaturated hydrocarbon radicals R2 of the diorganopolysiloxanes (A) and the silicon-bonded hydrogen atoms of the organohydrogenpolysiloxanes (C). Numerous suitable hydrosilylation catalysts are described in the literature. In principle, all hydrosilylation catalysts corresponding to the prior art and used in addition-crosslinking silicone rubber materials can be used.
For example, metals and their compounds such as platinum, rhodium, palladium, ruthenium and iridium, preferably platinum, can be used as hydrosilylation catalysts (E). The metals can optionally be fixed on finely divided support materials, such as active carbon, metal oxides such as alumina, or silica.
Platinum and platinum compounds are preferably used. Particularly preferred platinum compounds are those which are soluble in polyorganosiloxanes and are inert at a storage temperature up to 40xc2x0 C. but catalyze the hydrosilylation sufficiently rapidly on heating.
Preferred platinum catalysts (E) include those selected from compounds of the general formulae xe2x80x83Hxe2x80x94Cxe2x89xa1Cxe2x80x94(R14)fxe2x80x94Cxe2x89xa1Cxe2x80x94[xe2x80x94Pt(R11)xe2x80x94Cxe2x89xa1Cxe2x80x94(R14)fxe2x80x94Cxe2x89xa1Cxe2x80x94]exe2x80x94Hxe2x80x83xe2x80x83(8),
in which
R11 denotes an optionally substituted diene which is bonded to platinum by at least one xcfx80-bond and represents a straight or a branched chain having 4 to 12 carbon atoms or a cyclic ring having 6 to 18 carbon atoms,
R12 may be identical or different and denotes a hydrogen atom, trialkylsilyl radical, halogen atom or monovalent hydrocarbon radical optionally substituted by halogen atoms or cyano radicals and having 1 to 24 carbon atoms,
R13 denotes identical or different divalent, optionally substituted hydrocarbon radicals having 1 to 24 carbon atoms,
R14 may be identical or different and denotes divalent, optionally substituted hydrocarbon radicals having 1 to 12 carbon atoms, silane radicals or siloxane radicals,
R15 may be identical or different and denotes a hydrogen atom or a monovalent hydrocarbon radical having 1 to 20 carbon atoms,
e denotes an integer greater than or equal to 1 and
f is 0 or 1.
If R11 is a substituted diene or the radicals R13 and R14 are substituted hydrocarbon radicals, preferred substituents are halogen atoms, such as F, Cl, Br and I, cyano radicals, xe2x80x94NR152 and groups xe2x80x94OR15, R15 having the above-mentioned meaning.
Cyclooctadiene complexes of platinum having acetylide ligands, as described in EP-A-994 159, are particularly preferred, especially bis(alkynyl)(1,5-cyclooctadienyl)platinum, bis(alkynyl)(1,5-dimethyl-1,5-cyclooctadienyl)platinum and bis(alkynyl)(1,6-dimethyl-1,5-cyclooctadienyl)platinum complexes.
With the use of the platinum catalyst of the general formulae 5 to 8, the crosslinkable silicone compositions are marketable as a 1-component formulation and have a long shelf-life, in particular of at least 3 months at 25xc2x0 C. and ambient pressure, and crosslink rapidly only at a high temperature. In the preparation of the crosslinkable silicone compositions, it is especially advantageous that the platinum catalyst (E) of the general formulae 5 to 8 can readily be incorporated, that the hydrosilylation reaction does not slow down in the course of the reaction, and that no platinum colloids are formed and no discolorations result through their use.
Peroxide crosslinking agents (E) which may be used are inorganic and organic peroxides, in particular organic peroxides. Examples of such organic peroxides are peroxyketals, e.g. 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane and 2,2-bis(tert-butylperoxy)butane; acyl peroxides such as acetyl peroxide, isobutyl peroxide, benzoyl peroxide, di(4-methylbenzoyl) peroxide and bis(2,4-dichlorobenzoyl) peroxide; dialkyl peroxides such as di-tert-butyl peroxide, tert-butyl cumyl peroxide, dicumyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; and peresters such as tert-butyl peroxyisopropylcarbonate.
The self-adhesive crosslinkable 1-component silicone compositions preferably contain 10 to 90% by weight, more preferably 25 to 60% by weight, of diorganopolysiloxane (A); 10 to 80% by weight, more preferably 20 to 60% by weight, of filler (B); 0.1 to 20% by weight, more preferably 0.5 to 5% by weight, of organohydrogenpolysiloxane (C), and 0.1 to 10% by weight, more preferably 0.2 to 2% by weight, of organosilicon compound (D).
The amount of the hydrosilylation catalyst (E) used depends on the desired crosslinking rate and economic points of view. Usually, 1xc3x9710xe2x88x925 to 5xc3x9710xe2x88x922% by weight, in particular 5xc3x9710xe2x88x924 to 5xc3x9710xe2x88x923% by weight of platinum catalysts, calculated as platinum metal and based on the weight of the silicone compositions, are used.
The amount of the peroxide crosslinking agent (E) used is preferably 0.1 to 5% by weight, more preferably 0.2 to 3% by weight, based on the weight of the silicone compositions.
The self-adhesive crosslinkable 1-component silicone compositions can optionally contain further constituents (F), such as nonreinforcing fillers, inhibitors, stabilizers, pigments and catalysts. All components (A) to (F) may contain a single compound or a mixture of different compounds.
The self-adhesive crosslinkable 1-component silicone compositions preferably have a Mooney viscosity, determined at 25xc2x0 C. according to DIN 53523 Par t 3, of 15 to 150, more preferably 23 to 95.
The compounding of the self-adhesive crosslinkable 1-component silicone compositions is effected by mixing the abovementioned components in any desired sequence. The thermal crosslinking of the silicone compositions is effected by heating, preferably at 40 to 250xc2x0 C., more preferably at least 50xc2x0 C., most preferably at least 100xc2x0 C., preferably at not more than 200xc2x0 C., and most preferably at not more than 180xc2x0 C.
The invention also relates to the silicone elastomers obtainable by crosslinking the self-adhesive crosslinkable 1-component silicone compositions. The self-adhesive crosslinkable 1-component silicone compositions can be bonded to a substrate by applying the silicone compositions to the substrate followed by crosslinking, preferably by heating to 30 to 250xc2x0 C., to give a composite material, and can advantageously be used, in particular, wherever good adhesive strength between the silicone elastomer and a substrate, preferably a substrate of organic plastics, metals or glasses, is desired. The substrate may be present as a molding, film or coating.
The silicone compositions are suitable for the production of composite materials by coating, adhesive bonding, or casting, and for the production of shaped articles. The silicone compositions are particularly suitable for encapsulating and for adhesively bonding electrical and electronic components and for the production of composite moldings such as composite insulators for medium and high voltage applications. Composite moldings are understood as meaning a shaped article comprising a composite material which is composed of a silicone elastomer part produced from the silicone compositions and at least one substrate, so that there is a strong, permanent bond between the two parts. Such a composite molding is preferably produced by processing a metal or oxidic base element or organic plastic to give a shaped article and then bringing the silicone compositions into contact with this molding and crosslinking them, which can be effected, for example, by injection molding, by means of extrusion, and in a so-called press-molding method. These processes are exemplary and not limiting. Composite insulators are produced, for example, by sheathing rods or tubes of glass fiber-reinforced plastics. Composite materials and in particular composite moldings can be used in a very wide range of applications, for example, in the electronics, household appliances, consumables, construction and automotive industry, in medical technology, in the production of sport and leisure articles, etc.
In the following examples, unless stated otherwise in each case, all pressures are 0.10 MPa (abs.); all temperatures are 20xc2x0 C.; and all viscosities are measured at a temperature of 25xc2x0 C.